Latching solenoid valve

ABSTRACT

A pilot valve is operated by a solenoid formed by a coil wound around a non-magnetic spool that has a bore. A rare earth permanent magnet is inside the bore adjacent one end and abuts a flux concentrator farther inside the bore. A plunger is slidably located within the bore biased away from the flux concentrator by a spring and projects out another end of the bore. An enclosure of magnetic material completes a magnetic flux path around the solenoid and has an aperture though which the plunger projects. The pilot valve includes a cage of rigid non-magnetic material which abuts the enclosure and has a recess which supports the plunger out of contact with the housing. The plunger selectively opens and closes a pilot tube through the cage to operate a diaphragm the responds by engaging a primary valve seat to control the flow of fluid through a valve body.

FIELD OF THE INVENTION

The present invention relates to solenoid actuated valves; and moreparticularly to such valves with latching type solenoid actuators.

BACKGROUND OF THE INVENTION

In hospitals, public restrooms and other facilities, it is desirable toprovide a lavatory faucet which turns off automatically after a givenperiod of time, so that the water will not run indefinitely if the userdoes not shut off the faucet. Conventional faucets for this type ofoperation, typically are referred to as "metering faucets" and aremechanical in nature being operated by a piston. When the piston ismoved by the user to open the valve, a variable chamber within the valveexpands and fills with air or water. Upon being released by the user,the piston moves due to spring force and decreases the size of thechamber at a rate which is governed by the release of the air or waterthrough a metering orifice. This restricts the rate at which the springforce moves the piston to close the valve and thus the period that waterflows from the faucet. Among the draw backs with such a mechanicalfaucet is that the mechanical parts wear with repeated use and themetering orifice clogs, eventually requiring either replacement orperiodic adjustment and cleaning to ensure the valve remains open for asatisfactory period of time for the user to wash.

As an alternative to these mechanical automatic faucets, electricallycontrolled solenoid valve models have been proposed. However, aconventional solenoid valve remains open only while an electric currentis applied to an electromagnetic coil of the solenoid actuator. Uponremoval of the electric current, a spring forces the solenoid to closethe valve. As a result solenoid valves use a considerable amount ofelectricity which makes them impractical for battery powered operation.Therefore, power typically is supplied from the electrical wiring of thebuilding, thus requiring an electrical outlet underneath the lavatoryand protection against the user receiving an electrical shock in theevent of a circuit failure.

SUMMARY OF THE INVENTION

A general object of the present invention is to provide a latching typesolenoid actuator.

Another object is to provide such a latching solenoid valve with apermanent magnet located within an electromagnetic coil.

A further object of the present invention is to provide such a valvewhich is capable of being powered by a battery for a relatively longtime between battery replacement.

These and other objectives are satisfied by a latching solenoid whichhas a spool of non-magnetic material with a bore. A solenoid coil iswound on the spool to form an electromagnet that produces a magneticfield when an electric current flows through the coil. A permanentmagnet is located within the bore of the spool along with a fluxconcentrator of magnetically permeable material. A plunger is slidablylocated within the bore and projects axially outward from the spool.

A housing of magnetically permeable material encloses the spool and hasa first member that contacts either the permanent magnet or the fluxconcentrator. A second member of the housing has an aperture throughwhich the plunger extends without contacting the second member, tominimize friction effects on the plunger.

The solenoid operates a pilot valve mechanism that includes a cage ofnon-magnetic material is coupled to the housing and has a recess thatreceives and supports an end of the plunger. The cage includes a pilottube which has a passage having a first opening into the recess with apilot valve seat around that first opening.

A valve body is coupled to the housing and has an inlet and an outlet.The inlet communicates with the outlet through an aperture and a primaryvalve seat extends around that aperture. A resilient diaphragmselectively engages the primary valve seat to close the aperture. Theresilient diaphragm has a through passage within which the pilot tube istightly received.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section view through an automatic self-closing faucetwhich incorporates a latching solenoid valve according to the presentinvention;

FIG. 2 illustrates the valve and tubing sub assembly of the faucet; and

FIG. 3 is a cross sectional view of the latching solenoid valve.

DETAILED DESCRIPTION OF THE INVENTION

With initial reference to FIG. 1, a faucet 10 has a hollow body 12 witha spout 14 projecting upward and away from the main portion 13 of thehollow body. The body has a base plate 16 adapted to mount on thesurface of a lavatory or on a counter top adjacent a lavatory. The upperportion of the hollow body 12 has a cylindrical opening 15 whichreceives an actuator assembly 18 with a moveable top cap 20 that isslidably held in place by a screw 17 which enters a groove 19 in theactuator assembly core 21.

The actuator assembly 18 contains a battery 22 that is held against apair of electrical contacts 24 and 26 by cover 38 fastened to theassembly body 21 by another screw 39. The top cap 20 and cover 38 can beremoved easily to replace the battery without having to disconnect thefaucet 10 from the water supply or having to access components beneaththe surface on which the faucet is mounted. A printed circuit board 28,located within the hollow body 12, receives electric current from thebattery via the battery contacts 24 mounter thereon. A housing 49encloses the printed circuit board 28 providing protection againstmoisture damage and the screw 53 holding the housing in place alsosecures the actuator assembly 18 to the faucet body 12.

The printed circuit board 28 contains a timer circuit 29 and anelectrical switch 32 for triggering the timer circuit. A switch push rod34 extends downward through the actuator assembly 18 from just under theinside surface of top cap 20 to the switch 32 on the printed circuitboard 28. A spring 36 also biases the top cap 20 away from the cover 38and contact with switch push rod 34.

The electrical output of the timer circuit 29 drives a solenoid valve 30within the faucet housing 12. The solenoid valve 30 is connected to awater inlet tube 40 extending downward through the base plate 16 of thefaucet 10. A fitting 33 at the remote end of the inlet tube 40 containsa filter (not shown) which traps particles that could clod apertures ofthe solenoid valve 30. A tube 42 projects from solenoid valve 30 throughthe housing spout 14 to an outlet fitting 41 onto which an aerator 44 isthreaded. The solenoid valve 30, inlet tube 40, spout tube 42 and outletfitting 41 form an integral plumbing subassembly 45, as apparent fromFIG. 2, which nests within the hollow body 12 of the faucet 10 shown inFIG. 1. Water flows only through the plumbing sub-assembly 45 and doesnot come into contact with the faucet body 12.

The plumbing subassembly 45 is prefabricated and then inserted as a unitthrough the open bottom of the faucet body 12. During insertion thespout tube is pushed upward into the spout 14 until the subassembly'soutlet fitting 41 aligns with an opening 47 at the underside of theremote end of the spout 14. The aerator 44 then is screwed onto theoutlet fitting through the spout opening 47. The solenoid valve 30 ispushed upward until a flat beveled surface 43 abuts the housing 49 thatencloses the printed circuit board 28. Securing the base plate 16 acrossthe bottom opening of the hollow body 12 holds the plumbing subassembly45 in place with the inlet tube 40 projecting downward through that baseplate. This procedure is reversed to remove the plumbing subassembly 45for repair or replacement.

As will be described in greater detail, the top cap 20 is pusheddownward by a user to activate the faucet. That movement of the actuatorcap 20 presses push rod 32 downward, closing the switch 32 andactivating the timer circuit 29 on printed circuit board 28. While thetimer circuit is active, the solenoid valve 30 is in an open stateallowing water from the inlet tube 40 to flow through the aerator 44.

With reference to FIG. 3, the solenoid valve 30 comprises a latchingsolenoid actuator 50 having an outer housing 51 that encloses anelectromagnetic coil 52 wrapped around a spool 54 of non-magneticmaterial, such as a plastic. The outer housing 51 is fabricated of steelor other magnetically permeable material. The spool 54 has a bore 56extending centrally therethrough within which is received a cylindrical,metal flux concentrator 58 which has an annular groove with an 0-ring 60therein. The flux concentrator 58 is surrounded by the solenoid coil 52.A permanent magnet 62 abuts an end of the flux concentrator 58 and isadjacent an outer end of bore 56. The flux concentrator 58 and O-ring 60seal the bore of the spool 54 so that water in a lower portion of thevalve does not reach the magnet 62. As a consequence, a rare earthmagnet can be utilized which provides a relatively significant magnetforce for its size. A pole piece 64 is threaded into an integral fitting66 of the solenoid housing 51 and holds the magnet 62 within the spoolbore against the flux concentrator 58. The pole piece 64 can be adjustedaxially during assembly to compensate for manufacturing tolerances ofthe associated components.

A stainless steel plunger 68 is slidably located within spool bore 56 onthe opposite side of the flux concentrator 58 from permanent magnet 62and is biased away from the flux concentrator by a spring 70. The remoteend of the plunger 68 has a recess with a resilient seal 72 captivatedtherein. This remote end of the plunger 68 projects outward from aninternal end of spool 54.

That end of the spool 54 has outwardly extending flange 74 with anannular recess 76 extending around the opening of the spool bore 56. Acylindrical rim 78 of an end cap 80 of magnetically permeable material,such as stainless steel, is received within this recess 76 and is sealedthere against by a second O-ring 82. The open end of the housing 51 iscrimped around the edge of the end cap 80 which completes the enclosurefor the solenoid actuator 50. An aperture, which extends through thecylindrical rim 78, has a diameter that is slightly larger than theouter diameter of the plunger 68 which projects therethrough, therebyforming a magnetic flux gap 69. This results in the plunger 68 beingable to move axially without contacting the end cap 80. The end cap hasa second larger diameter tubular projection 84 extending outward fromthe opposite side.

The pole piece 64, outer housing 51, end cap 80, plunger 68 and fluxconcentrator 58 create a magnetic flux path for the permanent magnet 62and the electromagnet formed by coil 52. This flux path has a constantmagnetic flux gap 96 between the plunger 68 and the end cap 80, and avariable magnetic flux gap 67 between the flux concentrator 58 and theplunger 68. The size of the variable magnetic flux gap changes as theplunger moves within the bore 56 as will be described.

A plug-like cage 86, fabricated out of rigid non-magnetic material suchas plastic, has a closed end received within an opening of the secondend cap projection 84 to create a cavity 85 there between. This cavity85 is partially defined by a recess 90 in the cage 86 which receives theremote end of the plunger 68. The internal diameter of the recess 90closely matches the outer diameter of the plunger 68 to guide the axialmovement of the plunger while maintaining the outer surface of theplunger spaced from the magnetically permeable end cap 84. A thirdO-ring 88 provides a seal between the cage 86 and end cap 80. A bleedhole 87 provides a fluid passage from cavity 85 through the cage 86. Thecage 86 has a pilot tube 92 which projects downward beyond an open rim94 of the end cap 80. An aperture 96 through the pilot tube 92 has araised opening facing the plunger 68 thereby providing a pilot valveseat 98. The plunger seal 72 engages this pilot valve seat 98 when thesolenoid valve 30 is in the closed state, as will be described.

A diaphragm 100 of resilient material, such as rubber, extends acrossthe open rim 94 of the cage 86 forming a pilot chamber 115 therebetweenand is held in place by. The periphery of the diaphragm 100 iscompressed between the cage 86 and a valve body 102 that is threadedonto the end cap 84. The diaphragm 100 has a central aperture 104therethrough and the pilot tube 92 of the end cap fits tightly into thatcentral aperture. A central portion 106 of the diaphragm 100 resides inan inlet 114 within the valve body 102 and has a bleed aperture 107therethrough. In the closed state of the latching solenoid valve 30, thecentral portion 106 of the diaphragm 102 abuts a main valve seat 108formed around an opening of an outlet 110 from the inlet 114 to thespout tube 42. The water pressure in inlet 114 is communicated throughthe bleed aperture 107 so that the pressure in the cavity 85 behind thediaphragm 100 is greater than in the outlet 110, thus maintaining theaperture between the inlet and outlet at valve seat 108 closed.

In the closed state of the solenoid valve 30, the plunger 68 is heldagainst the pilot valve seat 98 at the opening of the pilot tube 92 bythe force of spring 70 and any pneumatic or hydraulic force present,whereby the plunger seal 72 closes that opening. The axial magneticforce exerted to draw the plunger 68 toward permanent magnet 62 isdetermined by the length of variable magnetic flux gap 67 between fluxconcentrator 58 and the plunger, as well as the flux density in thatmagnetic flux gap. That magnetic force is decreased by making themagnetic flux gap 67 larger or the flux density smaller. The design ofthe plunger 68, flux concentrator 58 and permanent magnet 62 causes thegap's flux density to drop rapidly as this gap length increases. In theclosed position of the plunger 68, the variable magnetic flux gap 67 issufficiently large that the axial magnetic force exerted by permanentmagnet 62 is minimized and can not overcome the spring force. Thus theplunger is latched in the closed position in the absence of electriccurrent flowing through the coil 52.

A substantially constant magnetic flux gap 69 exists in the magneticflux path between the plunger 68 and the end cap 80. The magnetic fluxin this gap creates a radial force on the plunger which can cause anundesirable friction which impedes axial movement of the plunger 68. Thepresent structure reduces the effect of this frictional force bysupporting the adjacent end of the plunger 58 on the plastic cage 86.That support holds the plunger nearly centered in the magnetic flux gap69 which minimizes the radial force and provides a low friction, lowwear surface against which the plunger slides. By supporting the plungerwith the plastic spool 54 and plastic cage 86, the constant magneticflux gap 69 can be made relatively small which improves the efficiencyof the latching solenoid actuator 50.

When a user presses the top cap 20 of the actuator assembly 18, thetimer circuit 29 is activated and applies a brief electrical currentpulse to the electromagnetic coil 52. The duration (e.g. 0.025 seconds)of this pulse is just long enough for the coil 52 to generate anadditional magnetic field of the same polarity as the permanent magnet62, which draws the plunger 68 farther into the coil spool bore 56 andaway from the pilot valve seat 98 at the opening of the pilot tube 92 asillustrated in FIG. 3. The current pulse is sufficiently intense thatthe plunger 68 strikes flux concentrator 58 thereby eliminating themagnetic flux gap 67 in the magnetic flux path and thus maximizes theforce from permanent magnet 62. This permanent magnet force issufficient by itself to overcome the force of spring 70 and hold theplunger away from the opening of the pilot tube 92. In other words, theforce from permanent magnet 62 now is greater than the spring force.Therefore the plunger is latched in the open state by the permanentmagnet 62 at the end of the electric pulse from the timer circuit 29 atwhich point the magnetic field produced by the coil 52 terminates.

The distance of the plunger stroke is kept relatively short to minimizethe energy required to move the plunger between the extreme positions ofits travel. This plunger stroke is adjusted by moving the pole piece 64into and out of the spool bore 56.

As the plunger 68 moves away from the pilot valve seat 98, the cagecavity 85 opens into pilot passage 96 which communicates with the spouttube 42. This relieves the pressure from within cavity 85 and within thepilot chamber 115 behind the diaphragm 100 via bleed hole 87. With thatpressure released, pressure within the inlet 114 forces the diaphragm100 away from the main valve seat 108 opening a passageway between theinlet and spout tubes 40 and 42. This allows water to flow through thevalve and out the aerator 44.

When valve open period (for example three to eleven seconds) lapses, thetimer circuit 29 automatically sends another pulse of electric currentthrough the electromagnet coil 52 in the opposite direction to that ofthe first current pulse thereby producing a magnetic field of oppositepolarity to that of permanent magnet 62. The timer circuit alsogenerates that pulse when the user operates the switch 32 by pressingtop cap 20 while the solenoid valve is open. This pulse produces anelectromagnetic field, which substantially cancels the permanent magnetforce, allowing the spring to force the plunger 68 out of the spool 54and against the cage 86, closing the pilot passage 96. That motion alsoincreases the variable magnetic flux gap 67 between the fluxconcentrator 58 and the plunger, so that at the end of the electricalpulse when the electromagnetic field terminates the force of thepermanent magnet is reduced to less than the spring force. As a resultthe spring 70 maintains the plunger in the closed state.

With the plunger 68 sealed against the pilot valve seat 98 at theopening of the pilot tube 96, pressure in the pilot chamber 115 behindthe diaphragm 100 becomes greater than the pressure in the outlet 110.As a result of this pressure differential, the diaphragm 100 is forcedagainst the main valve seat 108 thereby closing the passageway betweenthe inlet and spout tubes 40 and 42. The diaphragm 100 is maintained inthis position until pressure is equalized by the plunger 68 once againmoving away from the pilot valve seat 98. Because the plunger 68 engagesthe rigid cage 86 to close the pilot passage, it does not apply forcedirectly to the diaphragm 100. This results in a gentler, quieteroperation of the diaphragm.

What is claimed is:
 1. A latching solenoid valve comprising:a solenoidhaving a bore and a coil for producing a magnetic field when an electriccurrent flows there through; a permanent magnet located within the bore;a flux concentrator of magnetically permeable material located withinthe bore; a plunger of magnetically permeable material slidably locatedwithin the bore and projecting outward from the solenoid; an enclosureof magnetically permeable material containing the solenoid and having afirst member that contacts one of the permanent magnet and the fluxconcentrator, and a second member with an aperture through which theplunger extends; a cage of non-magnetic material coupled to theenclosure and having a recess into which an end of the plunger isreceived and supported, the cage including a pilot tube with a firstopening into the recess and with a second opening, the cage having apilot valve seat around the first opening and a bleed hole extendingthrough the cage from the recess; a valve body coupled to the enclosureand having an inlet and an outlet in communication through an aperturewith the inlet, wherein a primary valve seat extends around theaperture; and a resilient diaphragm cooperating with the cage to form achamber into which the bleed hole communicates, and responding topressure within the chamber by selectively engaging the primary valveseat to close the aperture, the resilient diaphragm having a pilotaperture which communicates with the outlet and within which the pilottube is received.
 2. The latching solenoid valve as recited in claim 1wherein the solenoid comprises a spool formed of non-magnetic materialabout which the coil is wound.
 3. The latching solenoid valve as recitedin claim 1 wherein the plunger has a resilient seal that selectivelyengages the a pilot valve seat.
 4. The latching solenoid valve asrecited in claim 1 wherein the flux concentrator includes a seal thatprevents fluid from flowing through the bore past the flux concentrator.5. A latching solenoid valve comprising:a housing of magnetic materialhaving an open end and a closed end with threaded aperture; a pole pieceis threaded into the threaded aperture; a spool formed of non-magneticmaterial within the housing and having a bore; a solenoid coil wound onthe spool for producing a magnetic field when an electric current flowsthere through; a permanent magnet located within the bore of the spooland abutting the pole piece; a flux concentrator of magneticallypermeable material located within the bore of the spool abutting thepermanent magnet; a plunger of magnetic material slidably located withinthe bore of the spool and projecting outward from the spool; a springbiasing the plunger away from the flux concentrator; an end cap ofmagnetic material engaging the housing and closing the open end, the endcap having an aperture through which the plunger extends withoutcontacting the end cap; a cage of rigid non-magnetic material coupled tothe end cap and having opposing first and second sides with the firstside having a recess within which an end of the plunger is received andsupported, the cage including a pilot tube having a pilot valve seat atone end which opens into the recess and having a second end, the cagefurther including a bleed hole extending between the recess and thesecond side; a valve body coupled to the housing and including an inletand an outlet in communication through an opening with the inlet,wherein a primary valve seat extends around the opening; and a resilientdiaphragm adjacent the second side of the cage to form a pilot chamberthere between, and responding to pressure within the chamber byselectively engaging the primary valve seat to close communicationbetween the inlet and outlet, the resilient diaphragm having a pilotaperture within which the pilot tube is received wherein the second endof the pilot tube communicates with the outlet.
 6. The latching solenoidvalve as recited in claim 5 wherein the spring is within the bore of thespool.
 7. The latching solenoid valve as recited in claim 5 wherein thepermanent magnet is a rare earth magnet.
 8. The latching solenoid valveas recited in claim 5 wherein the plunger has a resilient seal thatselectively engages the a pilot valve seat.
 9. The latching solenoidvalve as recited in claim 5 wherein the flux concentrator includes aseal that prevents fluid from flowing through the bore past the fluxconcentrator.